Effect of urophysial homogenates on plasma ion levels in Gillichthys mirabilis (Teleostei: Gobiidae)

In seawater-acclimated Gillichthys mirabilis, 2 and 4 hr after receiving an intraperitoneal injection of Gillichthys urophysial homogenate (two urophyses per fish), plasma sodium, magnesium, and chloride levels were significantly greater than those observed following a saline injection. When sodium and magnesium levels were measured in injected urophysectomized fish, similar increases were noted. No differences were observed in plasma potassium or calcium or in hematocrit between fish receiving saline and those receiving the urophysial homogenate. No differences were observed between urophysectomized and sham-operated fish in plasma sodium, potassium, calcium, and magnesium or in hematocrit 1, 3, 7, or 14 days postoperatively. Transection of the spinal cord at the level of the seventh or eighth preterminal vertebra had no effect on plasma sodium, potassium, calcium, or magnesium compared with sham-operated fish 14 days postoperatively. These findings demonstrate an effect of urophysial factor(s) on osmotic and ionic regulatory mechanisms in a euryhaline marine teleost.